In order to reduce power consumption many electronic components are now capable of operating at several power consumption levels, one of which is typically a power-down or sleep mode. The power-down mode is a low power consumption level that the component can enter into when it is not performing an operation and not being accessed. Reducing the level of power consumption is particularly useful for battery operated devices, such as portable computers, where reducing power consumption increases the battery life, and therefore the time the device can be used without having to either replace or recharge the battery.
A microprocessor consumes a significant amount of power in the full power-up mode, and it is typically accessed only a small portion of the time, therefore it is advantageous to bring the microprocessor into the power-down mode when it is not being accessed. In the power-up mode the microprocessor can draw a current of 10 A or higher. In the power-down mode, the microprocessor can maintain its state with a current of as little as 100 μA (i.e. as much as 100,000 less than in the power-up mode). A power supply, such as a battery, typically supplies the current to the microprocessor through a voltage regulator. The time in which the voltage regulator can go from delivering the proper voltage for the current required in the power-down mode to delivering the proper voltage for the current required in the power-up mode, and vis versa, is the transient response time of the voltage regulator. The large change in current demand of the microprocessor, which is the load of the system, may bring the system out of regulation during the transient response.
In some configurations proposed circuits have changed the bandwidth of the voltage regulator when the feedback loop of the voltage regulator indicated that the voltage regulator is out of regulation because of the large change in current demand. Alternative proposals have suggested monitoring circuits that could monitor the current demand of the load and notify the voltage regulator after there is a change in the current demand of the load.
A problem with the above methods is that during the time that the change in current demand is going through the feedback loop, or by the time the monitoring circuit detects that the current demand of the load has changed, the load is not receiving the appropriate voltage. The present inventor has observed that another problem with the above method is that during the time it takes to detect the change in the current demand the load is not receiving the proper voltage due to the large current demand, the voltage regulator does not know that it is not delivering the required voltage and has not even changed its bandwidth, thus increasing the transient response time by this amount of time.
Another problem with switching the frequency of the voltage regulator is that in order to get the required voltage quickly enough the frequency during the transient response has to be very high, typically on the order of 500 kHz or more. This requires high performance components, which are typically complicated and expensive.